MPP Solar MPI4K Inverter Review

We bought the MPP Solar MPI4K inverter from their authorized reseller maximum_solar via their store on ebay on 12th October 2016.
Due to delays it took almost a month to arrive from Germany and for this we got a 50 Euro refund.
When the inverter finally did arrive we plugged it into our 3000w solar array of 12 x 250w panels.

It worked perfectly for six months.

This summer we rewired our two solar panel arrays , instead of two disparate arrays ( 2000w and 3000w ) we now had two identical arrays of 2500w each.
According to the website and manual the MPI4K inverter is rated at a maximum of 5000w of solar power using two strings of ten panels.

4.65 KW from the solar panels

It worked fine for a day ( 2017-08-13 ) , when we came home later the inverter was schreeching and showing ‘Error 03’

I contacted support , filled in their spreadsheet with all the details and sent photos of the failed Q8 and Q7 mosfets we could see.

Failed Mosfets Q8 and Q7 in the DC-to-DC board of the MPP Solar MPI4K Inverter

We were told that the boards inside needed to be replaced , new boards would be sent out and that we would have to install them (?!).

We could see that this repair process was going to take some time so we ordered a second identical inverter , this would allow us to get back on solar power as soon as possible and later spread the load using the two inverters connected in parallel.

The replacement boards duly arrived , as the unit is under a year old and under warranty the exchange boards were free , but we still incurred an 80 dollar postage charge from Taiwan and a 38 Euro tax bill from the delivery driver. Nice.
Odd how the purchase on eBay included free delivery for the entire inverter yet carriage for two boards is 100 Euros. Dishonest.

Over the next last week I put the two replacement boards into the inverter case and carefully reconnected all the cables.

This morning ( 2017-09-09 ) we took the repaired inverter and put it back in place to tested it.
Thankfully I only plugged it into the mains electricity , not the load (our house) or the solar panels.
Unfortunately after a few seconds there was a loud pop and the display shows ‘Error 03’ again.

290V AC and the dreaded ‘Error 03’ again.

You can see in this photo that the AC grid value is showing 290V AC , unlikely a true mains electricity voltage reading – more likely a problem inside the inverter , this could explain why it blew up again.

After removing the top and sides of the case again I saw that the component QC1 on the AC input board has failed and exploded.

Another component failure in the MPP Solar MPI4K Inverter

2017-09-11 – Support have replied after the weekend , I have sent details and the photo of failed component QC1.

2017-09-14 – Support replied , asking for the same photo and the ‘unit current situation’ ?!

unit current situation ? – waiting for a month to be fixed!

2017-09-16 – Left negative feedback on eBay with a link back to this review.

2017-09-18 – Mailed Judy in Sales and Support again as nothing is happening.

2017-09-19 – Got a reply from Judy – “will pass on to Support”

2017-09-22 – Still no reply from either Judy or Support.

2017-09-23 – Our brand-new MPI4K inverter just exploded , I removed it and checked inside for damage , once again it is the mosfets on the DC to AC board , more damage this time though. We were only using a single solar string so the input could not have been more than 2500W , I checked it about an hour earlier and we were making about 1200W. After the failure I checked the voltage of the string – 300V DC , well within the tolerance of the inverter.


  • Low price
  • Nice green colour.
  • You get to disassemble and reassemble your own hardware!


  • Unable to handle the advertised 5000w of incoming solar power.
  • Free under warranty replacement boards actually costs over 100 Euros.
  • Over 1 month downtime per failure – 2017-08-13 to 2017-09-23 (still failed).

No response

I have contacted Bau-Tech four times now via both of their mail address in English and German and got no response at all , they seemed like a good company and I would have purchased from them for the next order , but this failure to even respond is worrying and unprofessional.

They were happy to accept the money , no interest in after-sales support.

German Quality.


It has been almost a week since Matthias Runne abandoned us and our solar kit installation after we gave him the final payment.

Continuing the project myself , I have started switching the house from mains electricity to the inverter only to find it too is not up to the task.

After (supposedly) 100s of hours of research and phone calls , Matthias Runne’s recommendation of a 3000w inverter is totally inadequate.

Strange that a ‘German Quality’ Solar Installer doing a proper site survey should have made such a fundamental error.

In 2015 I measured the electrical power usage of most of the equipment in our house and gave him these details during the site survey.

For example , our washing machine uses 2500w peak and our microwave uses 1150w.

Both of these devices cause the 3000w inverter to reset and are unusable.

In his incompetence he has also chosen a high frequency inverter where a low frequency one would suit our equipment better.

So much for the 100s of hours Matthias Runne supposedly spent calculating and specifying the solar kit we needed , when I powered on the washing machine for the first time the whole system died.

German Quality